Presently, the traditional scheme of power control device in electrical household appliance field is:
1) Employ a power supply unit (mainly switching power supply unit) as the standby power supply unit, power off most of the functional circuits, and still use the existing control and signal detection circuits (e.g., single-chip microcomputer and infrared receiving circuit) to control the standby power supply;
2) Employ an assistant AC power supply unit (linear power supply unit or switching power supply unit) as the standby power supply unit and control the standby power supply in conjunction with the existing control and detection circuits (e.g., single-chip microcomputer and infrared receiving circuit) or in conjunction with a separate standby power supply unit.
In the traditional scheme 1, the power consumption in standby mode comprises power consumption of the power supply unit and power consumption of the functional circuit of the controlled electrical appliance.
In one aspect, the inefficiency of the power supply unit and the functional circuit of the controlled electrical appliance under light load condition is a common problem in all power devices. Though the working efficiency of modern switching power supply units under rated load can be as high as 90% or above, the efficiency of those switching power supply units is still very low under light load, resulting in high standby power consumption. Though the standby power consumption of switching power supply units is reduced increasingly by utilizing low power consuming devices, materials, and leading control structures, such an improving process delivers poor results and the standby power consumption is reduced slowly; in addition, it strongly depends on the manufacturing level of fundamental electronic components and the latest design theories and methods for switching power supply units.
In addition, as the standby power consumption of a power supply unit is reduced gradually, the problem of standby power consumption of the functional circuit of the controlled electrical appliance becomes more and more prominent; as a result, reduction of standby power consumption also involves performing overall energy-saving design for all functional circuits of the controlled electrical appliance. Since the functional circuits of the controlled electrical appliance are usually complex, such renovation will cause increased workload, high technical risk, and longer time cycle of renovation. The energy saving design for specific electrical appliance is not applicable to other electrical appliances, and requires high financial investment and talent support. As increasingly strict standby power consumption standards are enacted, electrical household appliance companies will face great renovation pressure.
In traditional scheme 2, the ideal approach is to utilize the standby power consumption index of the controlled electrical appliance as the design index for rated working set-point of the assistant power supply unit (mainly switching power supply unit). In that way, the assistant power supply unit will be in a preferable load state when it is used to support standby function; since the efficiency is higher, the standby power consumption of the power supply unit may be very low. If lower standby power consumption is expected, the functional circuits of the controlled electrical appliance have to be renovated, or a separate standby power control circuit has to be utilized; as a result, the overall standby power consumption of the controlled electrical appliance can be reduced to a very low value. Apparently, such a scheme requires high direct cost and high renovation cost.
As the level of social civilization becomes higher and higher, more and more users (as high as 88%, as indicated by the sampling data from China Certification Center for Energy Conservation Products) favor standby mode. A fatal problem in AC power standby mode is that both the demanding operating environment of electrical household appliances and the weak structure of switching power supply units will result in severe potential safety hazard. That problem can't be overcome with traditional AC power standby schemes.
In view of above problems, many researchers have put forward solutions that employ a separate standby power control device, with the main idea as follows:
1) Before entering into the standby mode, physically cut off AC power supply to the controlled electrical appliance to shut it down completely, and then employ a separate standby power control device to control the standby process;
2) The standby power control device employs a non-AC power supply unit;
3) The power loss of the power supply unit itself can be neglected; the power consumption of the standby power control device in standby mode is the power capacity of the non-AC power supply unit.
That approach can achieve the following three effects:
1) The overall standby power consumption of the complete electrical appliance (measured externally) is equal to zero;
2) It implements intrinsically safe standby since the AC power supply is cut off completely;
3) Since the separate standby power control device is not complex, the power consumption can be very low. Therefore, the microscopic standby power consumption (power capacity of the non-AC power supply unit) of the controlled electrical appliance can be very low.
Viewed from the view point of AC power standby, the power consumption of the separate standby power control device in standby mode is now very low; as a result, the possibility and practicality of further reducing standby power consumption and the corresponding control structure are seldom investigated. More discussions focus on the power supply mode of non-AC power supply unit; the existing schemes include: storage battery, solar (photoelectric) battery, disposable battery, charged capacitor, and a variety of combined standby power supply schemes. Common problems in those schemes are: high complexity, increased cost, and a variety of problems in the special application environment of electrical household appliances.
For example, few people watch TV programs in darkness; therefore, the photoelectric battery scheme is almost feasible as long as the photoelectric battery can provide enough power to drive the relay. However, under the conditions of different light radiation angles and different radiation intensities, the user may feel apparent changes of control sensitivity of the remote controller, and thereby doubt the quality of the product.
The most possible storage battery scheme has three fatal defects:
1) The battery and the additional circuit may cause apparently increased cost;
2) The controlled electrical appliance must be started up before the end of the discharge cycle of the battery; otherwise the controlled electrical appliance can't be started up due to depletion of battery power. Any other remedial measure will increase operation complexity.
3) The most severe problem is: the service life of a storage battery doesn't match that of the controlled electrical appliance (for example, TV sets usually have a safe service life of 8-10 years).
Disposable Li—SOCl2 batteries have a service life of 10-15 years; theoretically, the service life of the battery can reach 10-15 years as long as the consumed power within the battery life is less than the power capacity of the battery. However, in order to minimize the battery cost, the overall standby current of the standby power control device must be reduced to a tiny level, which is apparently a very tough task.
The patent document “Power Saving Infrared Sensing System” (Chinese Patent No.: 98117670.4) disclosed a scheme that is closest to the ideal solution. The scheme is: in standby mode, the power control device itself is in sleep mode; an extremely low power-consumption front-stage induction circuit (referred to as an infrared on-duty circuit in this document) that is powered separately is used to monitor the lead code from the remote controller; once the lead code occurs, the power control device is woken up; then, the working infrared receiving circuit is activated to attain the expected control purpose.
That scheme tried to utilize the sleep mode of a single-chip microcomputer to reduce the standby power consumption of the control device; in addition, the inventor also recognized the problem of high standby power consumption of existing infrared receiving circuits (working infrared receiving circuit). The scheme attained the purpose of reducing standby power consumption by means of an “On Duty—Wake UP” mode.
However, the drawback in structure is that in sleep mode, the single-chip microcomputer and the peripheral circuit still produce power consumption, two infrared receiving circuits are required and the scheme for processing the power circuit (AC power supply switch) is not provided. The low power dissipation of the circuit makes no sense if the control of the AC power supply switch can't be settled effectively. The overall power consumption problem is that the standby power consumption not only comes from the control circuit and infrared receiving circuits, more important, it also comes from abnormal power loss in other parts of the system. For example, if there is no appropriate control structure, the battery has to supply power to the relay in the long term in case there is no AC power supply unit or the AC power supply unit fails during the process the controlled electrical appliance operates, resulting in severe battery power consumption. The structure of “front-stage induction circuit” itself is unable to provide very low standby power consumption as expected; therefore, it is difficult to employ a low capacity battery to supply power in the long term.
Viewed from functionality aspect the remote controller must support the cyclic code format of lead code 38 khz data codes. As a result, any general-purpose remote controller is not suitable; the bandwidth of on-duty circuit is too low, and thereby can only adapt to a few code formats. In addition, employing a disposable battery to supply power in the long term in Sleep—Wake-UP mode will cause the single-chip microcomputer to be unable to reset in long term due to power shortage. As a result, once the software system becomes disordered, the entire device can't be recovered to normal operation. Therefore, the scheme can't solve the problems substantially.